1. Field of the Invention
The present invention relates to a drill for forming bores in constructional components made of stone, concrete, break and the like and including a sleeve-shaped stem having an axially extending through-bore which opens into at least one mouth opening formed in a front end section of the stem, a shank provided at a rear end of the stem opposite the front end section of the stem for connecting the drill to a drilling tool, and a drilling head provided with lips and formed of a hard material and secured in at least one slot formed in a free end of the stem.
2. Description of the Prior Art
In addition to known drills for forming bores in constructional components of stone, concrete, break and the like, in which the drillings, which are formed during the drilling process are removed through at least one helical groove provided on a drill stem, in the past, so-called suction drills were used. They represent a drill with an axial bore which is connected with a vacuum-producing apparatus, in particular a vacuum dust collector, by an adapter and a coupling element. A suction drill should insure a high drilling capacity as a result of sucking of the drillings, which are formed during the drilling process, away and should provide for better cleaning of the bore. Such a suction drill is disclosed, e.g., in a German document DE-A-27 57 140. The known suction drill has a stem provided with an axial bore and having its end inserted in an adapter which is surrounded by a coupling element and, at the opposite end of the stem, a drilling head with a hard metal plate-like bit is releasably screwed in the stem. The suction bore is connected with a bore provided in the drilling head and which opens on opposite sides of the plate-like bit. The suction bore is connected, via the adapter and the coupling element, with a vacuum dust collector. During the drilling process, the formed drillings are transported away through the drilling head and the suction bore to the vacuum dust collector.
The known suction drill has a replaceable drilling head which is screwed in the stem. The drilling head is replaced upon wear of the hard metal bit or clogging of the mouth openings. When the known suction drill is used with a hammer drilling tool, the large single-blow energy of an axial impact results in an excessive loading of the helical thread in the stem and of the drilling head thread. The large single-blow energy of the axial impacts can lead to an excessive wear of both threads and, as a result, the connection of the drilling head with the stem is weakened. On the other hand, as a result of rotation of the drill during the drilling operation, the thread connection between the drilling head and the stem is so tightened that a very large force is required to unscrew the drilling head, if necessary, or that the drilling head cannot be unscrewed at all. Besides, the manufacturing of the known suction drill is rather expensive. Furthermore, the formation of an axial bore in a stem, which is made of a relatively long steel bar, sets high demand to the manufacturing technology.
To eliminate the drawbacks of the known suction drill and to facilitate its manufacturing, German Utility Model DE-U-79 08 923 proposed to form the drill stem of a steel sleeve. In the proposed suction drill, an end of the sleeve-shaped stem is connected with an adapter which is surrounded by a non-rotatable coupling element connected, e.g., with a vacuum dust collector. The adapter is also equipped with a shank which forms an axial extension of the stem and serves for connecting the drill with a drilling tool. The steel sleeve is provided at its opposite end with axial slots forming a cross-like pattern. A one-piece sintered cross-shaped bit formed of a hard metal is pushed into the axial slots and is secured there. The shape of the bit and the inner diameter of the sleeve-shaped stem are so selected that openings remain between the lips of the bit and the inner wall of the stem, which are connected with the axial channel formed in the stem.
The drill, which is disclosed in the German Utility Model De-U-79 08 923, has a relatively small stability in the region of the drilling head. The one-piece sintered cross-bit is supported only in the axial slots. The shearing forces, which are generated during the rotary-percussion drilling of a constructional component, act almost entirely on the cross-bit. As a result, the cross-bit can separate from slots, or the hard metal can burn out. The shape of the lips arranged in a cross-like pattern is so selected that, as it has already been discussed above, open regions remain between the lips and the stem inner wall.
These open regions extend along the axial channel or bore formed in the stem. The lips have a strip-like shape and have a height which increases toward the cross-shaped region. In this way, separate lips form, in the cross-shaped region, cutting points which span the axial channel without any support. During the drilling process, the projecting cutting points are subjected to a very large load as a result of application of axial blows. The shape of the cross-bit, in particular in connection with the use of the drill with a hammer drilling tool which is characterized, as discussed above, by a high single-blow energy of the axial impacts, can result in breaking of the one-piece sintered cross-bit. As it has also been discussed above, the openings, which are limited by the bit and the stem inner wall, are axially oriented. During the drilling process, the end of the drilling head can become completely submerged in the drillings. In this case, the suction action becomes insufficient for a quick removal of the drillings, and the opening could become clogged.
Accordingly, an object of the present invention is to eliminate the drawbacks of a suction drill disclosed in the prior art. Another object of the present invention is to provide a drill having a sleeve-shaped stem and a sintered drilling head which is formed entirely of a cutting material, preferably, of hard metal. A further object of the present invention is to provide a drill in which the danger of failure or breaking of the drilling head is substantially reduced. A still further object of the present invention is to provide a drill in which the attachment of the drilling head can be effected in a simple and reliable way. A yet another object of the present invention is to provide a drill in which clogging of the openings, which are provided in the front end section of the stem and which communicate with the stem through-bore, with the drillings is prevented.